In optical elements having an optical waveguide, in order to prevent the high-order mode light in the optical waveguide and the leaky mode light accompanying it (hereinafter, referred to collectively as “high-order mode light”) from causing the performance degradation of the optical elements, a high-order mode filter is known which reduces the high-order mode light. For example, Patent Literature 1 discloses a semiconductor laser diode in which a ridge portion is formed on the semiconductor substrate and grooves are formed between the ridge portion and clad regions which are located on the both sides of the ridge portion. The semiconductor laser diode realizes a single transverse mode by means of the configuration in which a top face of the clad region is located above the level of bottom faces of the grooves and a top face of the ridge portion is located above the level of the top face of the clad region.